1. Field of the Invention
The invention relates to a capacitive touch circuit.
2. Description of the Related Art
Nowadays, a capacitance sensor is widely used in different touch sensing devices such as a capacitive touch key, a touch panel, etc. Since different touch sensing applications have their respective suitable detection ranges of capacitance, and a suitable detection range of capacitance also varies according to the environmental condition, an external compensation device such as an external capacitor or resistor is used in the conventional design to vary the RC constant and hence the impedance of a relaxation oscillator. As a result, in order to obtain an optimum detection range suitable for different touch sensing applications and different environmental conditions, many capacitors or resistors having different values must be provided to improve the accuracy of capacitive touch sensing. Hence, the fabrication costs are increased and the adjustment to the impedance of the relaxation oscillator is inflexible. Further, in the conventional design, two comparators are used to perform charge and discharge operations for the relaxation oscillator to result in a complicated architecture of a touch sensing circuit.